test(libc): compare terminated strings at protected boundaries

core/libs/prx/libc/CMakeLists.txt

@@ -1343,6 +1343,16 @@ if(BUILD_TESTING)
             "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
     endif()
 
+    add_test_executable(guest_strcmp_boundary_tests ${LIBS_INCLUDE_DIR}/tests/GuestStrcmpBoundary.cpp)
+    target_include_directories(guest_strcmp_boundary_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(guest_strcmp_boundary_tests PRIVATE libc)
+    configure_windows_unwind(guest_strcmp_boundary_tests)
+    add_test(NAME guest_strcmp_boundary COMMAND guest_strcmp_boundary_tests)
+    set_tests_properties(guest_strcmp_boundary PROPERTIES TIMEOUT 20)
+    if(WIN32)
+        set_tests_properties(guest_strcmp_boundary PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
+    endif()
     add_test_executable(guest_heap_report_for_game_tests ${LIBS_INCLUDE_DIR}/tests/GuestHeapReportForGame.cpp)
     target_include_directories(guest_heap_report_for_game_tests PRIVATE ${LIBS_INCLUDE_DIR})
     target_link_libraries(guest_heap_report_for_game_tests PRIVATE libc)

core/libs/tests/GuestStrcmpBoundary.cpp

@@ -0,0 +1,99 @@
+#include "prx/libc/include/Api.hpp"
+#include <algorithm>
+#include <array>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <string>
+#include <vector>
+
+static void Require(bool condition) {
+    if (!condition) {
+        std::fputs("GuestStrcmpBoundary check failed\n", stderr);
+        std::abort();
+    }
+}
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <sys/mman.h>
+#include <unistd.h>
+#endif
+
+class Buffer {
+    unsigned char* allocation;
+    std::size_t page;
+public:
+    Buffer() {
+#ifdef _WIN32
+        SYSTEM_INFO info{};
+        GetSystemInfo(&info);
+        page = info.dwPageSize;
+        allocation = static_cast<unsigned char*>(VirtualAlloc(nullptr, page * 3, MEM_RESERVE | MEM_COMMIT, PAGE_NOACCESS));
+        Require(allocation != nullptr);
+        DWORD previous;
+        Require(VirtualProtect(allocation + page, page, PAGE_READWRITE, &previous) != 0);
+#else
+        const long size = sysconf(_SC_PAGESIZE);
+        Require(size > 0);
+        page = static_cast<std::size_t>(size);
+        allocation = static_cast<unsigned char*>(mmap(nullptr, page * 3, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
+        Require(allocation != MAP_FAILED);
+        Require(mprotect(allocation + page, page, PROT_READ | PROT_WRITE) == 0);
+#endif
+        std::memset(allocation + page, 0xa5, page);
+    }
+    ~Buffer() {
+#ifdef _WIN32
+        Require(VirtualFree(allocation, 0, MEM_RELEASE) != 0);
+#else
+        Require(munmap(allocation, page * 3) == 0);
+#endif
+    }
+    Buffer(const Buffer&) = delete;
+    Buffer& operator=(const Buffer&) = delete;
+    template<class T = unsigned char>
+    T* At(std::size_t count) {
+        Require(count <= (page - 32) / sizeof(T));
+        return reinterpret_cast<T*>(allocation + page * 2 - (std::max)(count, std::size_t{1}) * sizeof(T));
+    }
+};
+
+template<class T>
+static void Prefix(const T* data) {
+    for (int index = 1; index <= 8; ++index) Require(data[-index] == static_cast<T>(sizeof(T) == 1 ? 0xa5 : 0xa5a5));
+}
+
+static int Sign(int value) {
+    return (value > 0) - (value < 0);
+}
+
+int main() {
+    Buffer first, second;
+    for (std::size_t count = 0; count <= 128; ++count) {
+        auto* left = first.At(count + 1);
+        auto* right = second.At(count + 1);
+        for (std::size_t index = 0; index < count; ++index) left[index] = static_cast<unsigned char>(1 + (index * 73 + count) % 255);
+        left[count] = 0;
+        const std::vector<unsigned char> saved(left, left + count + 1);
+        for (std::size_t position = 0; position <= count; ++position) {
+            for (unsigned char value : {0, 1, 127, 128, 255}) {
+                if (position == count && value != 0) continue;
+                std::copy(saved.begin(), saved.end(), right);
+                right[position] = value;
+                int expected = 0;
+                for (std::size_t index = 0; index <= count; ++index) {
+                    if (left[index] != right[index]) { expected = static_cast<int>(left[index]) - right[index]; break; }
+                    if (left[index] == 0) break;
+                }
+                const std::vector<unsigned char> other(right, right + count + 1);
+                Require(Sign(strcmp_nid_postfix(reinterpret_cast<char*>(left), reinterpret_cast<char*>(right))) == Sign(expected));
+                Require(std::equal(saved.begin(), saved.end(), left));
+                Require(std::equal(other.begin(), other.end(), right));
+            }
+        }
+    }
+}